ADTs in Scala

gistfile1.scala

trait Maybe[A] {
  def apply[B](just: (=> A) => B, nothing: => B): B
}

object Just {
  def apply[A](a: => A): Maybe[A] = new Maybe[A] {
    def apply[B](just: (=> A) => B, nothing: => B) = just(a)
  }
  def unapply[A](a: Maybe[A]): Option[A] = a(Some(_), None)
}

object Nothing {
  def apply[A]: Maybe[A] = new Maybe[A] {
    def apply[B](just: (=> A) => B, nothing: => B) = nothing
  }
  def unapply[A](a: Maybe[A]): Boolean = a(_ => false, true)
}